Process for manufacturing dense shaped carbon articles



Patented Sept. 19, 1950 PROCESS FOR, MANUFACTURING DENSE SHAPED CARBONARTICLES Lloyd G. Swallen, Lombard, and Harold W. Nelson. Deer-field,Ill., assignors to Great Lakes Carbon Corporation, Morton Grove, 111., acorporation of Delaware No Drawing. Application May 25, 1948,

Serial No. 29,188

1 Claim. 1

This invention relates to an improvement in the manufacture of shapedcarbon bodies comprising calcined coke and a binder, and moreparticularly to producing carbon electrodes.

The methods of manufacturing carbon electrodes which are commonlyemployed commercially comprise mixing crushed calcined coke with abinder such as coal tar pitch or other bituminous tar or pitch, followedby molding or extruding the mixture into the desired shape using highpressures generallyin excess of 500 pounds per square inch. The greenelectrode thus made is baked and may be graphitized. In conventionalprocesses the coke is crushed to a desired particle size, usuallysmaller than inch depending on the size of the electrode. V

In the initial formation, coke flour comprising finely divided calcinedcoke particles is mixed with relatively larger coke particles orgranules in varying proportions to fill the spaces between the largerpieces; the coke aggregate is then thproughly mixed with the pitchbinder. Oil may be" added to assist in the lubrication during extrusion.

The calcined coke particles and coke flour employed is generallyproduced by heat ng petroleum coke or other low ash content cokes, at atemperature in a range of about 1000 to 1600 C. to reduce the volatilecontent below about 2%. The coke particles are made by crushing aftercalcination and are used as produced in the crushing operation. This iscarried out in the conventional type of grinding equipment such as jawcrushers, roller crushers, hammer mills and the like, leaving angularprojections on the pieces. The coke flour is made by pulverizing thefines obtained during the preparation of particles, so that 40-60%approximately, passes a 200 mesh screen.

The present invention relates to an improvement in the manufacture ofelectrodes which comprises subjecting the rough crushed coke particlesto attrition milling to more or less spherulize the particles butwithout substantially reducing their particle size. The spherulizedparticles are then used in the conventional manufacturing stepsemploying coke flour and pitch binder.

The calcining operation is carried out on lumps of the raw coke followedby crushing. The calcined coke is hard and brittle and upon beingcrushed in the jaw type crusher or similar apparatus breaks intoparticles having angular points and edges. The present operation causesthese angular projections to be attrited and the operation is carriedout in such a manner that little or no further crushing or reduction in(16? sired particle size occurs. 7

According to this invention the crushed coke particles are introducedinto an attrition mill which may comprise a drum containing bafiles orlifters and which can be rotated. The barrel of the mill may be set onan eccentric so that the particles during the rotation of the barrel arecaused to be lifted and rolled against one another as the operationproceeds. In this manner the sharp edges and points on the cokeparticles are broken or ground down. The milling should not be so severeas to cause substantial breakage of the particles themselves,.i. e.,breakage through the body of the particle. If this is done, the meshsize of the particles are reduced to an undesired extent. Since thesepoints or projections represent but a comparatively small proportion ofthe volume of each particle, grinding off the points reduces the weightof the particle by only a rela tively small amount and the averageparticle size as determined by screen analysis is substantiallyunchanged. The packing characteristics of the milled particles asevidenced by increased bulk density, are substantially improved. Thusfor example a calcined petroleum coke from. a Texas crude oil crushed to8 to 10 mesh had a gravity packed bulk density of 0.80. After tumblingthe granules in a cylindrical container equipped with bafiies, for aperiod of 360 minutes, using a cylinder speed of 100 revolutions perminute, the bulk density had increased to 0.91, or 114% of the original.Attrition of 10 to 14 mesh crushed coke particles from the same sourcegave a bulk density 113% of the original. 14 to 20 mesh particles of thesame coke were improved 117%. A screen analysis showed no substantialchange in the particle size of any of these. The minor amount of finesproduced was not over 3% of the original crushed particlesand could beincluded to replace a corresponding amount of coke flour in the finalelectrode mix.

In a similar manner tumbled 8 to 10 mesh particles of calcined coke froman Ohio crude oil had a bulk density 118% of that of the originalcrushed particles, with no substantial reduction in mesh size. Tumbled10 to 14 mesh particles from the same coke increased in bulk density to117% of that of the original crushed particles. The bulk density of 14to 20 mesh particles of the same coke were improved 121%.

Carbon electrodes were prepared from the coke from these two sources,using parts by weight of the 8-20 mesh coke, 40 parts of coke flour and26 parts of coal tar pitch binder. One part of otherwise identicalsamples which had not been tumbled.

These green electrodes were then subjected to baking by graduallyraising the temperature to about 1000 C. over a period of 8 days.Animprovement in the apparent density of the baked electrodes from Texastumbled coke was 102% of that of the electrode containing originalcrushed coke. The apparent density of tumbled Ohio coke electrodes was103% of the apparent density of the electrodes containing the.nontumblecl coke particles. At the same time an improvement inelectrical conductivity of the baked electrodes was noted, thisconductivity being 108% of that of the electrodes containing crushedunspherulized coke.

These baked electrodes containing tumbled coke were then graphitized byheating over a period of 3 days until a maximum temperature of '2800 C.was attained and showed an improvement in apparent density of 106% andan increase in electrical conductivity of 103% over electrodescontaining the untumbled coke particles. An improvement of this order isof substansistently obtained and the electrodes are consistently betterthan can be obtained by using the 'crushed coke particles themselves and(2) because the spherulizing operation is inexpensive and does not wastethe coke. The dust and fine particles formed clue to attrition can beincor porated in the mixture to be molded or extruded, as a part of theflour.

Even relatively small improvements in conductivity and apparent densityof baked or graphitized carbon electrodes, or anodes, are ofconsiderable commercial importance due to the fact that thiswrepresentsaisubstantial'decrease in power consumption because of their greaterconductivity. It also means that the shut-downs due to breakage andwearing away of the electrodes in electrothermal processes is reducedbecause of the increased strength of the electrodes or anodes made fromcoke particle components subjected to attrition milling.

Itshould bepointed out that the spherulizing operation as it -.is,hereinreferred to should not extend to a point where substantial reduction in'particleksize .of.the coke occurs but only to the extent that theprojecting or sharp edges are removed and the particles become rounded.

Any calcined coke suitable for electrode manufacture can be used in theprocess. Any suitable binder-which is known may also be employed.

"The processing conditions of electrode manufacture are otherwiseapplicable.

We claim as our invention:

A process for manufacturing hard, dense, shaped carbon articles whichcomprises crushing calcined coke, separating-fines, subjecting thecoarser particles to attrition milling-to remove the sharp edges andpoints therefrom without substantially reducing "the particle size,mixing "the milled particles with a pitch binder,

-forming the article in the desired shape and baking'it, thereby toproduce a hard, dense carbon article of higher apparent density andlower resistivity than is produced from the crushed coke without themilling treatment.

- LLOYD o; SWALLEN.

HAROLD w. NELSON.

"REFERENCES CITED Theyfollowing references are .of record in."the fileof this patent:

UNITED STATES PATENTS Number Name Date 1,086,503 Ayres Feb. 10, 19142,267,673 Cole Dec; 23', 1941 2,365,055 Cole Dec. 12, 1944

